Comparing bermudagrass and bahiagrass cultivars at different stages of harvest for dry matter yield and nutrient content

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1 Louisiana State University LSU Digital Commons LSU Master's Theses Graduate School 2006 Comparing bermudagrass and bahiagrass cultivars at different stages of harvest for dry matter yield and nutrient content Ryan Thomas Dore' Louisiana State University and Agricultural and Mechanical College, Follow this and additional works at: Part of the Animal Sciences Commons Recommended Citation Dore', Ryan Thomas, "Comparing bermudagrass and bahiagrass cultivars at different stages of harvest for dry matter yield and nutrient content" (2006). LSU Master's Theses This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Master's Theses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact

2 COMPARING BERMUDAGRASS AND BAHIAGRASS CULTIVARS AT DIFFERENT STAGES OF HARVEST FOR DRY MATTER YIELD AND NUTRIENT CONTENT A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Master of Science in The Interdepartmental Program of Animal and Dairy Sciences by Ryan Thomas Dore B.S., Louisiana State University, 2000 May 2006

3 Acknowledgements This thesis was made possible by the help of my major professor Dr. Dave Sanson, my on-campus advisor Dr. Don Franke, and committee member Dr. Jason Rowntree. I would also like to thank Dr. Brad Venuto for his input early in the planning phase of the project. I could not have achieved the lab work without the help of Dr. Lori Gentry, Dr. Cathy Williams, and Dr. Gayle Bateman. I would like to thank Dr. Howard Sonny Viator and Dr. Wayne Wyatt for allowing me to continue my duties as a beef cattle research associate while finishing my master s degree. Last but not least, I need to thank my family for the time and dedication that they have given me towards finishing my degree. ii

4 Table of Contents Acknowledgements... List of Tables. List of Figures Abstract.. ii iv vi vii Chapter I. Introduction... 1 Chapter II. Review of Literature 3 Introduction 3 Plant Structure 4 Forage Maturity. 7 Age and Maturity... 7 Leaf and Stem 9 Date of Cutting.. 10 Temperature.. 11 Chapter III. Materials and Methods Growing Time 13 Harvest Time.. 14 Chemical Analyses. 14 Data Calculations and Statistical Analysis. 14 Chapter IV. Results and Discussion Forage X Harvest Time.. 16 Season of Harvest X Cut Time.. 42 Chapter V. Summary and Conclusion 54 Literature Cited.. 58 Appendix: Supplementary Data 64 Vita. 79 iii

5 List of Tables 1. Dry matter (%) of bermudagrass and bahiagrass cultivars harvested after different growth periods Dry matter (kg/ha) of bermudagrass and bahiagrass cultivars harvested after different growth periods P values for model and contrast analysis for DM (kg/ha) of bermudagrass and bahiagrass cultivars Ash (%) of bermudagrass and bahiagrass cultivars harvested after different growth periods Ash (kg/ha) of bermudagrass and bahiagrass cultivars harvested after different growth periods P values for model and contrast analysis for ash (kg/ha) of bermudagrass and bahiagrass cultivars Crude protein (%) of bermudagrass and bahiagrass cultivars harvested after different growth periods Crude protein (kg/ha) of bermudagrass and bahiagrass cultivars harvested after different growth periods P values for model and contrast analysis for crude protein (kg/ha) of bermudagrass and bahiagrass cultivars NDF (%) of bermudagrass and bahiagrass cultivars harvested after different growth periods NDF (kg/ha) of bermudagrass and bahiagrass cultivars harvested after different growth periods P values for model and contrast analysis for NDF (kg/ha) of bermudagrass and bahiagrass cultivars ADF (%) of bermudagrass and bahiagrass cultivars harvested after different growth periods ADF (kg/ha) of bermudagrass and bahiagrass cultivars harvested after different growth periods 40 iv

6 15. P values for model and contrast analysis for ADF (kg/ha) of bermudagrass and bahiagrass cultivars Dry matter (%) of Russell bermudagrass harvested after different growth periods with different initial harvest dates Dry matter (kg/ha) of Russell bermudagrass harvested after different growth periods with different initial harvest dates P values for model and contrast analysis for DM (kg/ha) of Russell bermudagrass harvested at different starting dates Ash (%) of Russell bermudagrass harvested after different growth periods with different initial harvest dates Ash (kg/ha) of Russell bermudagrass harvested after different growth periods with different initial harvest dates P values for model and contrast analysis for ash (kg/ha) of Russell bermudagrass harvested at different starting dates Crude protein (%) of Russell bermudagrass harvested after different growth periods with different initial harvest dates Crude protein (kg/ha) of Russell bermudagrass harvested after different growth periods with different starting dates P values for model and contrast analysis for crude protein (kg/ha) of Russell bermudagrass harvested at different starting dates Neutral Detergent Fiber (%) of Russell bermudagrass harvested after different growth periods with different initial harvest dates Neutral Detergent Fiber (kg/ha) of Russell bermudagrass harvested after different growth periods with different initial harvest dates P values for model and contrast analysis for NDF (kg/ha) of Russell bermudagrass harvested at different starting dates Acid Detergent Fiber (%) of Russell bermudagrass harvested after different growth periods with different initial harvest dates Acid Detergent Fiber (kg/ha) of Russell bermudagrass harvested after different growth periods with different initial harvest dates P values for model and contrast analysis for ADF (kg/ha) of Russell bermudagrass harvested at different starting dates 53 v

7 List of Figures 1. Predicted DM production of bermudagrass cultivars over different periods of growth Predicted DM production of bahiagrass cultivars over different periods of growth Predicted ash production of bermudagrass cultivars over different periods of growth Predicted ash production of bahiagrass cultivars over different periods of growth Predicted crude protein production of bermudagrass cultivars over different periods of growth Predicted crude protein production of bahiagrass cultivars over different periods of growth Predicted neutral detergent fiber production of bermudagrass cultivars over different periods of growth Predicted neutral detergent fiber production of bahiagrass cultivars over different periods of growth Predicted acid detergent fiber production of bermudagrass cultivars over different periods of growth Predicted acid detergent fiber production of bahiagrass cultivars over different periods of growth Predicted DM production of bermudagrass cultivars over different periods of growth with different start dates Predicted ash production of bermudagrass cultivars over different periods of growth with different start dates Predicted crude protein production of bermudagrass cultivars over different periods of growth with different start dates Predicted neutral detergent fiber production of bermudagrass cultivars over different periods of growth with different start dates Predicted acid detergent fiber production of bermudagrass cultivars over different periods of growth with different start dates 78 vi

8 Abstract Rapid growth of warm-season grasses such as bermudagrass (Cynodon dactylon) and bahiagrass (Paspalum notatum) is associated with a decline in their nutritional value. This study was initiated to provide production and composition data with different cultivars of bermudagrass (common, Russell, Jiggs) and bahiagrass (Tifton-9, Pensacola, Argentina). Dry matter (DM), ash, crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) composition and production were evaluated every two weeks for a ten-week period on six different cultivars. Also, Russell bermudagrass was evaluated in a second trial very similar to the first trial for composition and production but was started at three different harvest times. Bermudagrass cultivars had higher DM (P < 0.05) than bahiagrass at all stages of maturity except for d 14. Dry matter production was less than 2000 kg/ha at the 14-d harvest for all of the cultivars. Jiggs produced more DM (P < 0.05) than the other grasses at 42-d harvest. Ash (%) decreased at a constant rate from day 14 until day 70. There was no significant difference (P > 0.05) among the three bermudagrasses and Argentina bahiagrass CP (%) at the 14-d harvest. Russell produced the least amount (P < 0.05) of CP at d 14, while Argentina produced the most CP. Russell, common, and Pensacola CP production (kg/ha) were similar (P > 0.05) and each were higher than Tifton-9 and Argentina after 42 days of growth. Bahiagrass NDF (%) was similar (P > 0.05) across the three cultivars at each of the different harvest times except for the 42-day harvest where Argentina had higher NDF levels (P < 0.05) than either Tifton-9 or Pensacola. The bahiagrass cultivars were similar (P > 0.05) in NDF production at 42 days. Jiggs produced more (P < 0.05) NDF than the other grasses at 56 and 70-d of growth. Common had the least amount of ADF at 56 and 70-d harvest (P < 0.05). ADF production was the highest (P < 0.05) in Jiggs from d 28 to d 70 of growth. Russell early- and mid-season harvest had greater vii

9 (P < 0.05) DM (%) and production than in the late season. Crude protein was the highest (P < 0.05) in both the early and mid season harvested Russell. The late season harvested Russell produced the least amount (P < 0.05) of DM and the least amount (P < 0.05) of CP. It was predicted that the late season harvested Russell would maintain DM and CP production at a constant rate for a longer period of time. This means that it would allow a producer a wider range of time to make hay or even graze this forage at that time of the year. viii

10 Chapter I Introduction Cow-calf operations dominate Louisiana s cattle industry. These operations are predominantly forage-based systems. The hot, humid summer days with adequate rainfall allow cattle producers to grow large amounts of warm-season forages such as bermudagrass (Cynodon dactylon) and bahiagrass (Paspalum notatum). These forages are C 4 grasses that are more metabolically efficient than temperate forages (C 3 ). C 3 plants fix energy into 3-carbon units and C 4 plants fix energy into 4-carbon units (Ball et al., 1996). Peak forage DM production occurs in midsummer, however, animal production is often depressed, due to decreased forage quality (Sollenberger et al., 1989; Sollenberger and Jones, 1989; Rusland et al., 1988). Beef producers face the problem of maintaining forage quality in an environment where forage production can change rapidly depending on several environmental factors. At times, when environmental conditions are favorable, harvesting (grazing or mechanical) within a timely manner can be very difficult. In times of drought, producing adequate levels of forages are difficult. Moving from medium quality to low quality can occur within a two to four wk period under certain conditions, making managing forage quality very difficult. In Louisiana, both cool-season and warm-season grasses often contribute to the forage supply. Warm-season grasses produce much edible dry matter, but generally they are of lower digestibility (Reid et al., 1988). In contrast, most cool-season grasses used in the state provide adequate nutrition even at a mature state. Warm- and cool-season grasses differ considerably in chemical and physical characteristics that can affect feed intake and digestion (Akin, 1986; Reid et al., 1988). The first study was initiated to provide composition and production data among different 1

11 cultivars of bermudagrass (common, Russell, Jiggs) and bahiagrass (Tifton 9, Pensacola, Argentina) at different stages of maturity grown under similar environmental conditions. The second study was initiated to compare season of harvest within harvest time of Russell bermudagrass. 2

12 Chapter II Review of Literature Introduction Warm-season grasses produce much edible dry matter, but are typically low in digestibility (Reid et al., 1988). Warm- and cool-season grasses differ considerably in chemical and physical characteristics that can affect feed intake and digestion (Akin, 1986; Reid et al., 1988). Warm-season grasses are generally lower in forage quality (crude protein (CP) and digestibility) at a given stage of maturity than temperate grasses due to a relatively low leaf-tostem ratio and chemical and physical characteristics associated with the C4 plants (Jones, 1985). Warm-season grasses also have rapid rates of maturation. Forage dry matter (DM) production of these grasses often peaks in mid-summer, however it is possible for animal performance (weight gains) to be depressed. This depression is related to decreased forage quality (Sollenberger et al., 1988). The predominant warm-season pasture grasses in Louisiana are bermudagrass (BEG) (Cynodon dactylon) and bahiagrass (BAG) (Paspalum notatum). Both bermudagrass and bahiagrass can tolerate a wide range of soil conditions and are commonly used for grazing and/or hay production. Bahiagrass is a warm-season perennial bunch grass native to South America. The Florida Agricultural Experiment Station first introduced common BAG to the US in Bahiagrass has several characteristics that make it valuable as a pasture grass. Bahiagrass grows on a wider range of soils than does bermudagrass. It usually will green up earlier and remain green longer in the fall than bermudagrass. A negative role of bahiagrass is that it lacks the drought tolerance of bermudagrass on deep sandy soils. It is recommended that bahiagrass should primarily be used for pasture, although some is harvested and conserved as hay (Redmon, 2000). 3

13 Bermudagrass has been part of southern agriculture for at least 250 years. Hybrid bermudagrass with improved productive capability and nutritive value has played an important role in livestock production across the southern US for nearly 60 years with the introduction of Coastal in 1943 by Dr. Glen Burton, USDA-ARS, Georgia Coastal Plains Experiment Station at Tifton, GA. Bermudagrass is a warm-season perennial that spreads mainly by rhizomes (underground stems) and stolons (horizontal aboveground stems). The grass tolerates a wide range of soil types and soil ph values, thus making it adapted to most of the southern US. Besides providing nutrition for cows during the growing season, bermudagrass also is harvested and conserved extensively as hay for livestock winter-feeding programs (Redmon, 2000). Plant Structure Plants derive energy from the sun, fixing carbon into their cellular structures. Distribution of this carbon and energy within a plant is greatly affected by environmental factors and the species of plant, thus forage quality is a combination of the environment and the genetic factors of the plant (Van Soest, 1982). There are two major functions of plant survival relevant to the nutritive quality of forage: storage of nutrients and defense against the environment. Plant reserves are needed for survival during periods of cold or drought and to provide nutrients for regrowth following defoliation, grazing, or cutting. These reserves are usually located in the highly digestible segments of the plant (cell soluble). Other structures such as lignin, cutin and secondary compounds are highly resistant to degradation and are usually associated with plant support and defense (cell walls). These structures by design are lower in digestibility and thus reduce the nutritive value of the forage. Thus, forage quality is primarily determined by its composition, or ratio of digestible and 4

14 indigestible components. Consequently, a sequence of cause-effect relationships exist among the environment and plant species (Van Soest, 1982). From an analytical standpoint, forages can be divided into 2 main components, the cell solubles and the cell walls. The cell solubles contain the portion of the plant that involves metabolism and growth of the plant. In contrast, the cell walls contain the portion of the plant that provides structure and protection (Van Soest, 1982). Ruminant animals have the ability to utilize vegetative plant material as their only source of nutrients (Hofmann, 1989). Unlike seeds, vegetative tissues contain a large percentage of their organic matter in the cell walls that provide structural integrity to the plant. The rumen allows for utilization of forages through a symbiotic relationship with microorganisms able to ferment the polysaccharides in plant cell walls and that are not amenable to mammalian enzymatic hydrolysis (Hungate, 1966). In other words, without the rumen and the relationship with the microorganisms that it houses, cattle would not utilize cellulose or hemicellulose in plants any better than humans. Fractionation of the carbohydrate component of forages is based on the system developed by Van Soest et al. (1991). The basis for this system is to break the carbohydrate components into fiber components (cell walls) and soluble components (cell solubles). The first step in this is conducting a NDF (neutral detergent fiber) analysis. This procedure refluxes the forage sample in neutral (ph = 7) detergent solution for 1 hour, which removes the solubles and leaves the fiber components. The primary components of the residue are hemi-cellulose, cellulose, and lignin. The next step is to reflux the sample in an acid (ph = 4.5) detergent solution. This procedure removes the hemi-cellulose fraction, leaving primarily cellulose and lignin in the residue. 5

15 The cell-wall fraction of plants has been implicated as a control mechanism for forage intake by ruminants (Waldo, 1986). A reduction in the concentration of cell-wall material may improve both intake and energy density of forages. Increased digestibility of the cell wall would improve energy availability. The plant cell wall is a complex biological structure containing many different molecules whose biosynthesis is controlled by enzymes encoded and regulated by genes (Iiyama et al., 1993). The different methods of fiber analysis are analytical product which describe those forage components that have low solubility in specific solvent systems and less digestible than starch. In some cases, such as mature grasses, the cell wall and fiber concentrations of forages are very similar, whereas for legumes the fiber estimates are routinely lower than the cell-wall concentration (Theander and Aman, 1980). Although all plant cell walls have a similar basic architecture, there are important differences among the major taxonomic groups of forages in details of wall composition and structure. Legume leaves contain much less cell wall than do leaves of grasses, and legume leaves do not exhibit the increase in cell-wall concentration associated with maturation of the plants that occurs in grass leaves (Wilman et al., 1977; Wilman and Altimimi, 1984). Stem material of all forages is higher in cell-wall concentration than their leaves, and stems always increase in wall content with maturity (Griffin and Jung, 1983; Albrecht et al., 1987; Jung and Vogel, 1992). Lignin is the major component of the cell wall that is recognized as limiting digestion of the cell wall polysaccharides in the rumen. Lignin seems to exert its negative effect on cell-wall polysaccharide digestibility by shielding the polysaccharides from enzymatic hydrolysis (Jung and Deetz, 1993). Lignin s influence of fiber digestibility has been shown to be greater in grasses than in legumes (Smith et al., 1972; Buxton and Russell, 1988). 6

16 Forage Maturity Forage yield and nutritional qualities of pasture are influenced by numerous factors representing ecological conditions and management activities. Those factors include frequency of cutting, species composition, plant maturity, climatic conditions, soil fertility status, and harvest season (Van Soest, 1982). The two most influential factors that affect forage quality and forage utilization are forage species and forage maturity. According to Van Soest (1982) as a pasture matures, fiber and lignin contents are high while protein content is low. When comparing temperate grasses to tropical grasses, tropical forages usually have increased annual dry matter yields. Changes of quality during the growing period of grasses are particularly high under tropical climatic conditions (Nelson and Moser, 1994). The maturity of forages plays a key role in the clearance of rumen material. Clearance of digesta from the rumen is the primary process that affects forage intake by ruminants (Ulyatt et al., 1986). This process depends largely on digestion by ruminal microorganisms and on rate and extent of particle size reduction (Moseley, 1982). According to Moseley (1982), any type of forage particle must be reduced to a specific size before it can exit the rumen. Age and Maturity Forage quality can be described by a plants development due to its stage of growth. Plant maturity is defined as the morphological development culminating in the appearance of the reproductive cycle: tillering, flowering, pollination, and seed formation. Plant age is generally defined as the period since the beginning of regrowth in spring following winter, or growth of aftermath following the time of cutting or grazing. Some factors that may accelerate the maturation process are high temperature, longer periods of light, water, and soil fertility; those 7

17 that retard it are clipping, grazing, disease, drought, lower temperature, less periods of light and soil fertility (Van Soest, 1982). Forage age greatly influences physiological plant maturity; however, the relationship can be greatly modified by individual plant responses and environmental factors. Johnson et al. (2001) observed that forage mass had a quadratic relationship with harvest date, with peak forage mass occurring in late June and July. Sumner et al. (1991) compared year-round bahiagrass yield on nine south Florida ranches and reported that peak yields occurred during midsummer (late July). Additionally, Chambliss et al. (1999) and Mislevy (1999) reported that peak mass for bermudagrass and stargrass occurred during midsummer (late July). Age and maturity of plants affect the intake level as well as animal performance. Phillips et al (2002) reported that 82% kenaf hay pellets harvested 58 days post planting were successfully used to replace alfalfa pellets without decreasing intake, N balance, or performance of crossbred wethers less than 1-yr old and weighing 36.4 kg. Rinne et al. (2002) reported that increased maturity reduced silage and total DM intake and milk yield, while effects on milk composition were minor. Earlier harvest of grass lowered ruminal fluid ph and increased VFA and ammonia concentrations. The proportion of butyrate to other VFA decreased with advancing maturity, but effects on propionate proportions were less consistent. Ruminal fluid protozoa decreased with advancing maturity of grass silage (Rinne et al., 2002). Summer grasses can be left alone and not harvested for hay production in the late summer or early fall. This is considered to be stockpiled forage. A trial was conducted in Overton, Texas where six seeded bermudagrass cultivars, two bahiagrass cultivars, and a kikuyugrass cultivar were compared with Coastal and Tifton 85 bermudagrass in a small plot study. The trial was looking at these grasses as a potential for grazing stockpiled forage after the 8

18 first frost. Evers et al. (2004) reported that Tifton 85 had greater autumn standing forage mass than bahiagrass and kikuyugrass. Crude protein concentrations declined slowly from October to February and were always above the minimum requirements for a nonlactating pregnant cow. Acid detergent concentrations among the bermudagrass, bahiagrass, and kikuyugrass increased with time. Bahiagrass cultivars always had some of the highest ADF concentrations, which suggest they may not be the best warm-season perennial grass for stockpiling (Evers et al., 2004). Leaf and Stem Forage maturity is frequently associated with less leafiness and an increasing stem-to-leaf ratio. Stems are usually associated with lower-quality components than the leaves on forages; however, this is not always true. Alfalfa and many other legumes species use the stem as structural components (lower-quality) and the leaves as metabolic organs (higher-quality). In contrast, grasses use leaves for both structure through the lignified midrib and as metabolic organs. Thus, the nutritive value of alfalfa leaves will be maintained during the aging process where as grass leaves will decrease in quality (Van Soest, 1982). However, in some grasses, the stem is considered to be a reserve organ and this will lead to the stems having a higher quality than the leaves. For example, timothy and sugarcane utilize the stem as a reserve organ (Van Soest, 1982). Newman et al. (2002) showed that canopy height of continuously stocked limpograss pastures affects herbage N fractionation and degradation parameters. The lag time for CP degradation from all canopy heights was much longer than reported for temperate forages and somewhat longer than other C4 grasses. 9

19 Date of Cutting The date for obtaining an optimum (economically and financially feasible) yield of digestible matter varies and is relatively later in the northern US compared to the southern US and is later in regions of higher elevation. Higher environmental temperature encourages lignification and more rapid physiological development so the forage will become less nutritive. Thus, first harvest of forages is generally higher in quality due to lower temperatures. The second cuttings are usually lower in digestibility than the first cuttings of the same chronological and physiological ages (Van Soest, 1982). Flores et al. (1993) reported that Pensacola bahiagrass had only 48% leaf blade when determining total forage DM for June harvested grass when compared to 89% leaf blade in Mott elephant grass. The remainder of the June harvested Pensacola grass was mainly seed stalks (peduncle plus inflorescence). Interactions and inconsistencies among grasses and seasons existed. For example, June-harvested Pensacola had less digestibility but approximately 6% higher NDF intake than September-harvested Pensacola. Apparently, greater lignin concentration in seed stalks of June-harvested Pensacola decreased in vivo digestibility but did not decrease small-particle passage or voluntary intake. Johnson et al. (2001) studied NDF concentrations in several species over the growing season. They found a linear increase for NDF concentration in bahiagrass across the harvest season. In contrast, peak levels of NDF in bermudagrass occurred after late June well before harvest. They also found a cubic response for NDF in stargrass with peak levels being observed in late June and September. Mandebvu et al. (1996) observed an inverse relationship between lignin concentration and in-vitro dry matter digestibility (IVDMD) for Tifton 85 bermudagrass. 10

20 The 7-wk Tifton 85 forage had lower IVDMD than the 3½-wk grass due to greater maturity. The chemical composition of kenaf hay is greatly influenced by harvesting date. Philips et al. (2002) evaluated kenaf fed as freshly harvested forage and as silage and reported DM digestibility ranging from 58.9% to 82.4%, depending on the date of harvest. In another experiment, the in situ disappearance of OM and N fractions of kenaf harvested at different intervals after planting were evaluated. At 62 days after planting, OM in situ disappearance was 73.7%, and N disappearance was 85.5% (Phillips et al., 1996 and 1999). Temperature The temperature during forage growth plays a major role in the nutritive value of the forage. Lower digestibility at higher temperatures is the result of the combination of two main effects. Increased lignification of plant cell wall is an effect of higher environmental temperatures, and enzymatic activities associated with lignin biosynthesis are enhanced by increased temperature. A higher environmental temperature also promotes more rapid metabolic activity, which decreases the pool size of metabolites in the cellular contents. Temperature has its greatest effect on plant development in promoting the accumulation of structural matter. Higher environmental temperatures have little effect on the alfalfa leaf, but the stems will increase in percent lignin and the leaf-to-stem ratio may decrease. In contrast, grasses will decline drastically in nutritive value with increased temperatures since the leaves serve as support as well as metabolic function. Both the leaf and stem quality of grasses decline with increasing temperature, and this effect is more pronounced in tropical grasses (Van Soest, 1982). Leaf quality declines particularly as a result of lignification of the midrib, which contains the major portion of the lignin of grass leaves (Deinum, 1976). In an additional study, Deinum et al. (1968) reported a decline of half a unit of digestibility per degree Celsius increase in temperature 11

21 when light, age, maturity, and fertilization were controlled. Johnson et al. (2001) reported that in-vitro organic matter digestibility (IVOMD) was highest in early June for bermudagrass, bahiagrass, and stargrass than any other harvest time. A midsummer reduction of approximately 10.3% in IVOMD was observed during July when each of these grasses were less than in early June. In August, IVOMD improved for all three forages due to the fact that autumn was approaching. Rusland et al. (1988) found a similar digestibility pattern in limpograss (Hemarthria altissma). Sollenberger et al. (1989) reported that the greatest forage digestibility of limpograss and Pensacola bahiagrass occurred with either spring or autumn growth and that IVOMD of bahiagrass was typically reduced during the summer. A decrease in digestibility of 7.6% for bermudagrass and 12.9% for bahiagrass has been reported when temperatures increased from 26 to 35 C (Henderson and Robinson, 1982). The negative relationship between digestibility and temperature may be caused by a reduction in the leaf-to-stem ratio and increased proportion of the indigestible fractions. This is due to increased metabolic rates of the plant associated with increased temperatures (Nelson and Volenec, 1995; Henderson and Robinson, 1982). Henderson and Robinson (1982) reported a positive relationship between NDF and temperature for bermudagrass, while also reporting a negative relationship in bahiagrass between NDF and temperature. This was due to the leaf-to-stem ratio that bermudagrass contains versus bahiagrass. Increased ADF concentrations for bermudagrass and bahiagrass were positively correlated with higher temperatures (Henderson and Robinson, 1982). 12

22 Chapter III Materials and Methods A trial was conducted to evaluate the effect of growing time on forage production and forage quality with three cultivars of both bermudagrass (BEG) and bahiagrass (BAG). Bermudagrass cultivars evaluated were Russell, Jiggs, and common. Bahiagrass cultivars evaluated were Argentina, Pensacola, and Tifton 9. A second trial was conducted to evaluate the effects of harvest time within the season on forage production and forage quality with Russell bermudagrass. Growing Time Forages (common, Russell, Jiggs, Tifton-9, Pensacola, and Argentina) were established at the Rosepine Research Station in the summer of Common bermudagrass and the three bahiagrass varieties (Tifton-9, Pensacola, and Argentina) were planted on a prepared seedbed with pure live seed. Common bermudagrass seed was broadcasted at 5.6 kg/ha. Bahiagrass varieties were broadcasted at a seed rate of 16.8 kg/ha. Russell and Jiggs bermudagrass were vegetatively propagated on a prepared seedbed. Soil type was Ruston fine sandy loam. On June 21, 2001, all the plots were cut with a disc mower, the forage removed and 112 kg/ha of N, 44.8 kg/ha of P 2 O 5, and kg/ha of K 2 O was applied per hectare. The fertilizer was a complete mixture of dry fertilizer and was applied with a Gandy dribble box applicator. Subsequently, the plot area was clipped the same day with a lawn mower to a stubble height of 2.54 cm. Each of the 6 cultivars was divided into 30 plots of approximately 1.83 m by 6.1 m. Five harvests were made at 2 wk intervals beginning July 5, On harvest day, 6 plots of each cultivar were harvested. A 1.22 m by 6.1 m strip (7.44 sq meters) was harvested down the center using an Almaco sicklebar harvester. The forage was clipped to a 5 cm stubble height. The 13

23 forage from each subplot was weighed and served as the harvested plot weight. A random sample was taken from the harvested material. The sample was weighed (averaged approximately.91 kg) and dried at 70 C for 120 hrs. Dried samples were then ground through a Wiley mill with a 1 mm screen for laboratory analysis. Plot dry matter yields were calculated for each subplot based on the dry matter factor determined from drying each random sample. Harvest Time Three replications of 30 plots of Russell bermudagrass were assigned to be harvested at two wk intervals, but each set of plots had a different start date. One was identical to those used in the cutting time trial. Start dates for the other two sets of plots were July 19, 2001and August 16, Plot management and sample collection procedures were the same as in the cutting time trial. Chemical Analyses Samples were analyzed for dry matter by drying in a forced air oven (110 C) for 24 hrs (AOAC, 1990). Subsequently, the sample was ashed with a muffle furnace (600 C) for at least 2 hrs (AOAC, 1990). Crude Protein (CP) was obtained using Kjeldahl-N procedures (AOAC, 1990). Samples were digested for 2 hrs on a block digestor at 385 C, cooled under a fume hood, distilled with a 2200 Kjeltec Auto Distillation unit and then titrated for NH 3. Samples (0.5g) were analyzed sequentially for neutral detergent fiber (NDF) and acid detergent fiber (ADF) using the procedure described by Van Soest et al., (1991), except that the ANKOM fiber analyzer with filter bags was used. Data Calculations and Statistical Analysis Plot production data is presented as kg/ha and is based on the fresh weight of each plot times the dry matter factor obtained by drying a sample of the plot harvest at 70 C for 120 hrs 14

24 and converting to a kg/ha basis. The conversion from lbs/ac to kg/ha was obtained by dividing the lbs. of forage by and then multiplying by In both trials, data were initially analyzed using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC) in a split plot design. The model compared forages within time. Forage type was the main plot and harvest date (interval) was the sub-plot. Interactions among forage species and growing time were present (P < 0.05) for most variables, thus data were subsequently analyzed within growing time as a one-way analysis of variance. The design of the second study was a 3 by 5 factorial with start date and growing time as the main effects. Means were separated using lsd procedures. Data were also analyzed by time within forage cultivar (SAS, 2002). Orthogonal contrast for linear, quadratic, and cubic effects were used to evaluate the effect of growing time within forage type. The REG procedure of SAS was used to develop prediction lines (SAS, 2002). 15

25 Chapter IV Results and Discussion Forage X Harvest Time Dry Matter Composition and Production Bahiagrass DM composition (%) was similar (P > 0.05) across the three cultivars at each of the different harvest times except that Argentina had a lower DM content when harvested at 56 days then the other two cultivars (Table 1). Bermudagrass cultivars were more variable, and had higher DM (P < 0.05) than Bahiagrass at all harvest times except for 14-d. Dry matter production was less than 2000 kg/ha at the 14-d harvest (Table 2) for all of the cultivars and would probably not be economical for commercial harvest at this time. Argentina bahiagrass produced (P < 0.05) the most DM at the 14-d harvest, followed by Jiggs bermudagrass and Pensacola bahiagrass. There was no difference between (P > 0.05) Pensacola and Tifton 9 bahiagrass, although DM production by Jiggs was higher (P < 0.05) than Tifton 9. Common bermudagrass produced more DM (P < 0.05) than Russell but less than the other forages. At the 28-d harvest, Jiggs bermudagrass and Argentina bahiagrass produced more DM (P < 0.05) than the other grasses (Table 2). There was no difference (P > 0.05) in the amount of DM produced among the other grasses at the 28-d harvest. Jiggs produced more DM (P < 0.05) than the other grasses at the 42-d harvest. There was no difference (P > 0.05) in DM produced among the other grasses at this harvest. Jiggs maintained (P < 0.05) its DM production advantage at the 56-d harvest. Dry matter production was similar (P > 0.05) among the other grasses except for Pensacola bahiagrass 16

26 Table 1. Dry matter (%) of bermudagrass and bahiagrass cultivars harvested after different growth periods. Bermudagrass Bahiagrass Days of growth Russell Common Jiggs Tifton-9 Pensacola Argentina SE Prob a 26.0 b 22.4 c 26.3 b 25.9 b 24.9 b 0.6 < a 32.7 a 33.2 a 30.9 b 30.7 b 29.3 b 0.8 < a 41.3 a 39.6 a 27.6 b 28.4 b 27.6 b 0.7 < a 45.9 b 46.9 b 32.2 c 30.2 c 25.3 d 0.9 < a 28.4 b 28.1 b 25.1 c 24.8 c 24.2 c 0.7 <.0001 abc Row means with different superscripts are different (P < 0.05). 17

27 Table 2. Dry matter (kg/ha) of bermudagrass and bahiagrass cultivars harvested after different growth periods. Bermudagrass Bahiagrass Days of Growth Russell Common Jiggs Tifton-9 Pensacola Argentina SE Prob a 574 b 1212 c 1019 d 1131 dc 1715 e 75 < a 4251 a 6720 b 4255 a 4713 a 5949 b 344 < a 6826 a 8629 b 6309 a 6273 a 6750 a 312 < a 7557 a b 7148 a 5660 c 7416 a 479 < ab 6600 a 8981 c 7737 b 7512 ab 8818 bc abc Row means with different superscripts are different (P < 0.05). 18

28 which produced less DM (P < 0.05) than any other forage. Jiggs bermudagrass produced more DM (P < 0.05) than all other grasses except for Argentina bahiagrass at the 70-d harvest. Dry matter production was not different (P > 0.05) among the three bahiagrass cultivars. Common bermudagrass produced (P < 0.05) less DM than the bahiagrass cultivars, but the level was not different (P > 0.05) than DM produced by Russell bermudagrass. There was no difference (P > 0.05) in DM produced among Russell bermudagrass and the bahiagrass cultivars. Contrast analysis of DM production within forage indicated a quadratic function (P < 0.001) for all bermudagrass cultivars (Table 3). Prediction lines (Figure 1) indicated a similar growth pattern for both common and Russell bermudagrass, with the production tending to separate after 40 days. The prediction line for Jiggs bermudagrass indicates a higher rate of production throughout the trial. All three cultivars tended to peak in production around 60-d. Hill et al. (1993) reported that a new high-yielding bermudagrass hybrid, Tifton 85, produced Table 3. P values for model and contrast analysis for DM (kg/ha) of bermudagrass and bahiagrass cultivars. Model Linear Quad Cubic Russell <.0001 <.0001 < Common <.0001 <.0001 < Jiggs <.0001 <.0001 < Tifton 9 <.0001 <.0001 < Pensacola <.0001 <.0001 <.0001 <.0001 Argentina <.0001 <.0001 <.0001 <

29 26% higher DM yield (P = 0.05) with 11% higher IVDMD (P = 0.05) than Coastal in two 3-yr trials. Tifton 85 and Jiggs bermudagrass are similar in their physical makeup. They both contain larger stems with bigger leaves. While DM production of Tifton 9 bahiagrass resulted in a quadratic expression (P < 0.05), both Pensacola and Argentina bahiagrass had a cubic pattern of growth (Table 3). The prediction line for Tifton 9 (Figure 2) indicates a similar DM production pattern to both common and Russell bermudagrass. In contrast, both Argentina and Pensacola prediction lines indicated a higher rate of DM production during the early portion of the trial, a slower production during the middle of the trial then an increase towards the end. The prediction lines indicate that Argentina would be expected to have the highest level of production in the first 50 days of growth. Ash Composition and Production Bahiagrass ash composition was similar (P > 0.05) across the three cultivars at each of the different harvest times (Table 4). Jiggs bermudagrass had the highest ash composition (P < 0.05) at day 14, while ash composition of common bermudagrass was higher than the bahiagrass cultivars, but not different than Russell bermudagrass. There was no difference (P > 0.05) in ash composition among any of the grasses for the rest of the harvest times. Argentina bahiagrass and Jiggs bermudagrass produced (P < 0.05) the most ash at the 14- d harvest (Table 5). There was no difference between (P > 0.05) Tifton 9 and Pensacola bahiagrass, but both of these grasses had higher ash production (P < 0.05) than either common or Russell bermudagrass. Russell bermudagrass had the lowest (P < 0.05) ash production at 14 days of harvest. 20

30 Table 4. Ash (%) of bermudagrass and bahiagrass cultivars harvested after different growth periods. Bermudagrass Bahiagrass Days of growth Russell Common Jiggs Tifton-9 Pensacola Argentina SE Prob ab 8.0 b 9.4 c 6.7 a 7.1 a 7.4 a 0.3 < abc Row means with different superscripts are different (P < 0.05). 21

31 Table 5. Ash (kg/ha) of bermudagrass and bahiagrass cultivars harvested after different growth periods. Bermudagrass Bahiagrass Days of growth Russell Common Jiggs Tifton-9 Pensacola Argentina SE Prob 14 25a 46 b 114 c 70 d 81 d 126 c 6. < a 301 a 430 b 273 a 290 a 425 b a 326 a 501 b 352 a 312 a 378 a a 421 a 542 b 383 a 286 c 413 a abc Row means with different superscripts are different (P < 0.05). 22

32 At the 28-d harvest, Jiggs bermudagrass and Argentina bahiagrass produced more ash (P < 0.05) than the other cultivars (Table 5). There was no difference (P > 0.05) among the other four cultivars at this harvest time. Jiggs bermudagrass continued to produce more (P < 0.05) ash than the other grasses at d 42 and d 56. At the 42-d harvest, there was no difference (P > 0.05) among the other five grasses. Pensacola bahiagrass produced (P < 0.05) the least amount of ash at 56 days. There were no differences (P > 0.05) in ash production by Russell or common bermudagrasses, or Tifton 9 and Argentina bahiagrasses during this d 56 harvest. Ash production was not different (P > 0.05) among the six cultivars at the d 70 harvest. Russell bermudagrass resulted in a cubic expression (P < 0.05), while both common and Jiggs bermudagrass had a quadratic pattern of growth (Table 6). Russell and common bermudagrass tended to follow the same pattern early in the growing phase (Figure 3). Russell bermudagrass tended to reach its peak in ash production earlier than common. In contrast, Jiggs Table 6. P values for model and contrast analysis of ash (kg/ha) of bermudagrass and bahiagrass cultivars. Model Linear Quad Cubic Russell <.0001 <.0001 < Common <.0001 <.0001 < Jiggs <.0001 <.0001 < Tifton 9 <.0001 < Pensacola <.0001 <.0001 < Argentina <.0001 <.0001 <

33 bermudagrass increased in ash production at a more rapid rate from 14 days until approximately 42 days. Once Jiggs bermudagrass peaked in ash production at approximately 45 days, ash production of this forage decreased. Ash production of Tifton 9 bahiagrass resulted in a quadratic expression (P < 0.05), while Pensacola and Argentina had a cubic pattern of growth (Table 6). Argentina bahiagrass had a higher rate of ash production than Pensacola bahiagrass (Figure 4). Argentina bahiagrass had a higher peak in ash production than did either Pensacola or Tifton 9. Crude Protein Composition and Production There was no difference (P > 0.05) on the three bermudagrass cultivars and Argentina bahiagrass CP composition at the 14-d harvest (Table 7). Both Pensacola and Tifton-9 bahiagrasses had lower CP composition at the 14-d harvest. Crude protein composition of the bermudagrass cultivars was not different (P > 0.05) at 28 days of growth. Likewise, bahiagrass cultivars were similar (P > 0.05) in CP at this time. Crude protein composition of the bermudagrass cultivars were higher than the CP of the bahiagrass cultivars at 4 wk growth. Arthington and Brown (2005) reported similar results when they compared bermudagrass to limpograss and bahiagrass. Crude protein composition of Tifton 9 bahiagrass was similar to all of the other grasses (P > 0.05). At the 42-d harvest, Russell bermudagrass and Pensacola bahiagrass had higher levels (P < 0.05) of CP than the other grasses (Table 7). Common bermudagrass had higher CP content (P < 0.05) than Argentina bahiagrass but was not different (P > 0.05) from Jiggs bermudagrass or Tifton 9 bahiagrass. There was no difference in the CP composition (P > 0.05) among Jiggs bermudagrass, Tifton 9 bahiagrass or Argentina bahiagrass. There was no difference in CP among the different grasses at 56 and 70 days of growth. 24

34 Table 7. Crude protein (%) of bermudagrass and bahiagrass cultivars harvested after different growth periods. Bermudagrass Bahiagrass Days of growth Russell Common Jiggs Tifton-9 Pensacola Argentina SE Prob a 20.8 a 20.8 a 17.6 b 17.0 b 19.1 a a 11.3 a 11.4 a 10.7 ab 10.3 b 10.1 b a 8.7 ab 8.0 bc 8.2 bc 9.1 a 7.4 c abc Row means with different superscripts are different (P < 0.05). 25

35 Arthington and Brown (2005) suggested that averaging over all grasses in their study, increased forage maturity was associated with 37.8% less CP concentration compared with harvesting at 4-wk growth. Similarly, we observed that there was a 39.9% decrease in CP when harvesting at 10 weeks of growth rather than at 4 weeks. According to Brown and Mislevy (1988), other researchers have reported that average tropical forage CP content decreases below 9% after 6 wk of summer growth. Likewise in our study, at the 42-d harvest, common, Jiggs, Tifton-9, and Argentina were all below 9% CP. Russell and Pensacola were reported as having 9.0 and 9.1% CP, respectively after 6 wks of growth. According to Gates et al. (2001), Pensacola bahiagrass exceeded Tifton-9 in CP concentrations on 5 different harvest dates. This was consistent with previous findings of Mislevy et al. (1990), who demonstrated that CP concentrations were higher in Pensacola than in Tifton-9 bahiagrass. Conversely, our data suggest that Pensacola and Tifton-9 were similar in CP concentrations accept at the 42-d harvest. Hill et al. (1993) reported that mean masticate analyses revealed similar CP for Tifton 78 and Tifton 85 in May, and July, but higher (P < 0.05) CP for Tifton 85 than for Tifton 78 in September. Sanderson et al. (1999) reported that crude protein concentrations decreased from 113 g kg 1 at the May harvest to 79 g kg 1 in the second regrowth harvest taken in July. It was also reported by Sanderson et al. (1999) that CP concentrations decreased as the final harvest was delayed. Twidwell et al. (1988) observed a decrease in CP from 170 to 100 g kg 1 at ages ranging from 0 to 28 d after appearance of leaf material in switchgrass. These findings are similar to what was observed in the present research. This pattern was the result of plant aging, as forage quality of switchgrass typically decreases with maturity (Burns et al., 1997). 26

36 Russell bermudagrass produced the least amount (P < 0.05) of CP at d 14, while Argentina bahiagrass produced the most CP (Table 8). Jiggs bermudagrass produced more CP (P < 0.05) than Russell, common, Tifton 9, and Pensacola bahiagrass. Tifton 9 and Pensacola bahiagrass were similar (P > 0.05) in their CP production at 14-d harvest and produced more CP than common bermudagrass. At the 28-d harvest, Jiggs bermudagrass produced the most CP followed by Russell bermudagrass and Argentina bahiagrass (P < 0.05) (Table 8). There was no difference (P > 0.05) in CP production among common bermudagrass, Tifton 9 bahiagrass, and Pensacola bahiagrass. Jiggs bermudagrass also produced more CP (P < 0.05) at the 42-d harvest than the other grasses, with production levels 12.4% and 14.1% higher than Russell and common bermudagrass, respectively. Russell bermudagrass, common bermudagrass, and Pensacola bahiagrass CP production were similar (P > 0.05) and these grasses had higher production (P < 0.05) than Tifton 9 and Argentina bahiagrass after 42 days of growth. There was no difference between Tifton 9 and Argentina bahiagrass (P > 0.05) in CP production at 42 days. By d 56, Jiggs bermudagrass produced the most CP (P < 0.05), followed by Russell and common bermudagrass (Table 8). Harvested CP was not different (P > 0.05) among common bermudagrass, Tifton 9, and Argentina bahiagrass at the 56-d harvest. There was no difference (P > 0.05) between CP produced at 56 days between Pensacola and Argentina bahiagrass. Crude protein production was not different (P > 0.05) among any of the grasses at the 70-d harvest. 27